Conventionally, it is known that an assembling unit has a first tubular portion, a second tubular portion and a sealing member which is disposed between the first tubular portion and the second tubular portion air-tightly and liquid-tightly. US-2005-0047937A1 (JP-Patent No. 4203909) shows a fuel-vapor-leakage check system in which a first tubular portion is integrally formed with a suction portion of a vane pump. Moreover, a second tubular portion has an annular groove on its outer wall. An annular shaped sealing member made of rubber is disposed in the annular groove. The second tubular portion with the sealing member is inserted into an interior of the first tubular portion, so that an assembling unit is formed.
In the above fuel-vapor-leakage check system, when the second tubular portion with the sealing member is inserted into the first tubular portion, an inner periphery of the sealing member is in contact with the annular groove and an outer periphery of the sealing member is in contact with an outer wall surface of the first tubular portion. When the first tubular portion and the second tubular portion relatively move in their axial direction, the sealing member is rotated in such a manner that the inner periphery moves toward the outer periphery and the outer periphery moves toward the inner periphery.
In the fuel-vapor-leakage check system shown in US-2005-0047937A1, the first tubular portion and the second tubular portion are formed cylindrical. Moreover, before the sealing member is engaged with the groove, an inner diameter of the sealing member is slightly larger than an outer diameter of the groove. Thus, when the sealing member is engaged with the groove, a strained force of the sealing member is uniform around the second tubular portion. Moreover, before the sealing member is engaged with the groove, a cross sectional shape of the sealing member is circle. That is, the sealing member is an O-ring. Therefore, when the second tubular portion with the sealing member is inserted in first tubular portion, the sealing member is rotated equally without respect to its circumferential position. It is considered that no twist is generated in the sealing member.
In recent years, it has been required that a fuel-vapor-leakage check system including a vane pump is reduced in its size. For example, when a thickness of the vane pump is reduced, an axial length of a cam ring is reduced. That is, a height of the cam ring is lowered. In a case that a suction portion is formed in an outer wall of the cam ring, it is necessary to form the suction portion based on the height of the cam ring in order to ensure a fluid passage area of the suction portion. That is, it is necessary that the suction portion is a non-perfect circle
In a case that the first tubular portion is integral with the suction portion of the vane pump, it is necessary that the cross sectional shapes of the first and the second tubular portion correspond to the shape of the suction portion. When the sealing member is engaged with the second tubular portion of which cross sectional shape is a non-perfect circle, the strained force of the sealing member is not uniform around the second tubular portion. Therefore, when the second tubular portion with the sealing member is inserted in first tubular portion, the sealing member is rotated unequally with respect to its circumferential position. It is likely that a twist may be generated in the sealing member
A twist of the sealing member may cause deterioration in airtightness and liquid-tightness between the first tubular portion and the second tubular portion. Such deterioration also causes deterioration in suction performance of the vane pump falls, whereby a detection accuracy of the fuel-vapor-leakage may be deteriorated.